Hello jondecker76,
Sounds to me like you MIGHT have gotten a bargain, although new panels are available for a dollar a watt these days. With new panels you get a tax credit of 30 cents per watt, reducing your cost without shipping to 70 cents per watt. You'd still have to pay shipping, and so unless you can use the tax credit and/or can get free or low cost shipping, I'd say you probably got a bargain. My first set of panels, back in 1978, were BPs, same brand as yours. They disappeared off my sailboat into the Sea of Cortez during a storm in 1982. I don't know if you can get the tax credit when you buy previously-owned panels, but if it were me, I'd go for it and let the IRS ding me if they disagreed.
I notice they were manufactured in 2002. Nominal 48 volt panels that small in wattage size were a little unusual back then, and still are; but not impossible to find. The picture of the nameplate doesn't show the nominal voltage. Are you sure they're nominal 48 volts? Doesn't really matter as long as you know what it is; since they are all alike you can connect them in series-parallel combination to get almost any voltage you want, as long as it's greater than the nominal voltage of a single panel and less than the input dc voltage of your charge controller. You'd be better off if they were 12 volt, 42 watt panels, or 48 volt higher wattage panels (see reason below).
During a year's time the sun's maximum elevation angle at high noon will vary plus or minus 22.5 degrees from whatever it is at high noon on the vernal and autumnal equinoxes. At high noon on the vernal and autumnal equinoxes the sun's elevation angle will be equal to your latitude. At the summer solstice the sun's elevation angle will be your latitude plus 22.5 degrees. At the winter solstice the sun angle will be your latitude minus 22.5 degrees. The amount of energy your fixed PV array receives from the sun decreases if the array is not pointed directly at the sun. But it decreases as the cosine of the difference angle. The cosine of 0 degrees (i.e., sun at a 90 degree angle to your array, difference angle equals zero) is 1. You get 100 percent of the sun's available energy. But let's say the sun is shining at a 10 degree angle to your array at high noon. The cosine of 10 degrees is .985, so you haven't lost much. You are still getting 98.5 percent of what you would have gotten if the sun was shining directly on your array.
Solar panels are so cheap these days that it almost doesn't pay to try to maximize their output by adjusting their angle to the sun, especially for large arrays. Just slap 'em down pointing straight south and forget about adjusting them, that would be my advice. For small arrays, say up to a thousand watts, it might be worth the trouble to seasonally adjust them. Dual axis trackers cannot be economically justified these days unless there are space and/or zoning constraints, or you're a techno-geek. I have 1.4 kw of Sharp 175 watt panels mounted on a Wattsun dual axis tracker. I get a kick out of watching it follow the sun all day, then spin around after the sun goes down and park itself pointed at where it thinks the sun is going to come up in the morning. Doesn't take much to amuse me, these days.
Let's see. Your 41 degrees latitude plus 15 degrees (to equalize winter and summer performance) equals 56 degrees, which is the optimum angle (measured between the plane of the ground and the plane of the PV array) at which you should mount your array. A roof with an 18:12 pitch is at an angle of 56 degrees. If there's any chance that you have the need and enough space on your property for a shed, that's what I'd recommend. A shed with a south-facing roof big enough to hold that 2 kw array. Sheds are cheap compared to angle iron and go up a lot faster. No welding needed. You could make it a pole-shed (even cheaper) if your zoning allows. The poles can be anchored in cement. In my zoning area, no building permit is necessary for a shed under 200 square feet, which would be large enough for a 2 kw array with the roof angled at 56 degrees. Then you got someplace to put the lawnmower and all of that other junk that most of us stuff our garages full of and then have to leave the new car outside.
I'm not going to comment here on how you should connect these panels to each other and then to your combiner box, and then to your MPPT controller (You do plan to use one of each of those, right?), because I am sure others on this forum who know as much or more about that as I do will comment. Besides, I can't (nor can anybody else) tell you how to connect those panels unless they know what controller you are going to use; specifically what it's maximum dc input voltage is. If nobody comments, let me know and I can help you. You DO NEED to use a combiner box with a breaker position for each series string that you end up with. You want to configure the array so that you end up with the least number of series strings, yet do not have a string that is so long that it is capable of exceeding the maximum dc input voltage of your charge controller. If these panels truly are 48 volt nominal voltage 42 watt panels, and you are charging a 48 volt battery bank, you're going to end up with a BIIIG combiner box with lots of breakers. It'd be better if they were 48 volt 200 watt panels or 12 volt 42 watt panels. If they were 12 volt panels you could combine 4 or more panels (depending on the controller) into a series string, then you'd only have ten or less strings.
It gets kinda complicated, in a hurry. You need to choose a charge controller before you do much of anything else. Pick the one that has the highest possible dc input voltage and enough amperage capacity to control 2 kw of PV panels.
I hope some of the more knowledgeable folks on this forum will analyze my post and tell you if I have steered you in the wrong direction. I'm getting senile, my finest days are behind me, it's cocktail hour as I write this, and it'd sure be nice if somebody could check what I've written and maybe put you back on the straight and narrow path.
Additional comments on your post:
"small (<1000 AH) 48 volt battery bank for back up power"
That is a huge battery bank, with 2 kw of solar and a wind turbine feeding it. I wouldn't go over 500 AH at 48 volts. Batteries are EXPENSIVE, you'll be looking at around $8 - $10 per AH. Use the leftover money for more generating capacity, either wind or solar.
". . .essentially the grid is my dump load. . ."
The grid works great as a dump load as long as your generating capacity never exceeds your inverter's sell capacity and the grid never goes down while the wind is blowing. If you have a wind generator you still need a (resistance heating) dump load for those times when the wind is blowing hard and the grid is down.
"My thought was to have the grid tie inverter wired directly to the battery bank, and turn it on when the batteries are full . . ."
You won't have to turn it on; any UL-listed, correctly programmed inverter (such as the Outback GVFX 3648) will automatically sell to the grid when the batteries are charged, and stop selling to the grid when the batteries are discharged.
poco
Six phases in the life of man, starting at birth:
- Sleeping, drinking, and pooping.
- Eating and guns.
- Eating, rock and roll, drinking, guns, and sex.
- Money, drinking, guns, and sex.
- Money, drinking, guns, and pooping.
- Sleeping, drinking, and pooping.
